Abstract
The integrated photovoltaic/thermal collector (PV/T) with solar assisted heat pump (SAHP) often operates under an undesigned condition. Against the backdrop of heat pump system oscillation resulting from the mismatching between collectors area and compressor capacity, this work explores the dynamic performance of heat pump system at a fixed compressor frequency when the condensing water temperature and electronic expansion valve (EEV) opening are variable or invariable. We also consider why the system is unstable and propose the theory of SAHP system stability. Also, a preliminary performance analysis is made on SAHP system that is respectively influenced by an inverter compressor and EEV. The MSS(Minimum Stable Signal) line theory is proposed to account for system unstabilty in the research of the match between EEV and evaporators, that is to say, the critical problem of keep the system stability is to find out how evaporators superheat under the circumstance of specified loads and its corresponding EEV opening, in other words, to find the MSS line.
Highlights
The solar assisted heat pump (SAHP) system combines a solar collector and a heat pump for the purpose of improving the coefficient of the performance (COP) of a heat pump and the efficiency of its thermal collectors
With a compressor of a rated capacity, a heat pump assists an evaporator in extracting thermal energy primarily from solar energy that varies over different seasons or even different times of a day
As the variation of solar radiation becomes intensified, it is hardly possible for a constant-frequency compressor to meet the demand of a SAHP system under a dynamic condition
Summary
The SAHP system combines a solar collector and a heat pump for the purpose of improving the coefficient of the performance (COP) of a heat pump and the efficiency of its thermal collectors. An inverter compressor is able to make an SAHP system operate under a better condition by changing the frequency of the system as the solar radiation differs. Through a full-year forecast of SAHP system that applied an inverter compressor, researchers like Chaturvedi suggest that the COP of a heat pump and thermal efficiency of its collectors, and the system premium operating performance can be guaranteed by converting the frequency of the compressor to an optimal performance according to weather status in different seasons throughout the whole year [1]. Qu Ac τα ηel G Tf m Ta mr cp N Tp hwind εp εg is the heat loss of collector’s top (W{pm2 ̈ ̋C)) is the thermal conductivity of heat insulating layer at the bottom of the collector (W/m K) is the thickness of heat insulating layer at the bottom of the collector (mm) is the thermal conductivity of lamination layer at the bottom of the collector (W/m K) is the thickness of lamination layer at the bottom of the collector (mm) is the space between heat-absorbing tubes (mm) is the diameter of heat-absorbing tubes (mm) is the collector’s efficiency factor is the collector’s heat transfer factor is the coefficient of heat convection between refrigerant within the tube and the tube wall (W/m2 ̈ K) is collector’s effective yield (W) is the solar panel area (m2) is the product of penetration rate and absorption rate of solar perpendicular incidence and diffuse radiation against the solar panel is the photoelectric conversion efficiency is solar irradiation intensity is the average temperature of refrigerants within tubes of the collector ( ̋C) is the environment temperature ( ̋C) is refrigerants’ mass flow (kg/s) is the specific heat capacity under a constant pressure (kJ/(kgk)) is the number of overlying layers is the temperature of heat-collection plates ( ̋C) is the coefficient of heat convection caused by wind (W/m2 ̈ K) is the emissivity of heat-collection plates is the emissivity of the glass layer β is collector’s inclination angle Vwind is the wind speed (m/s)
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